function parallel(fns, done) {
  const results = {};
  fns.forEach((fn, index) => {
    fn((result) => {
      results[index] = result;
      if (Object.keys(results).length === fns.length) {
        done(results);
      }
    });
  });
}

const parallel = async (funcArray) => new Promise((resolve, reject) => { 
  const resultArray = []
  let summary = 0
  funcArray.map((p, i) => Promise.resolve(p).then((value, error) => {
    if ( error )
      reject(error)
    
    resultArray[i] = value
    if ( ++summary === funcArray.length )
      resolve(resultArray)
  }))
})

function parallel(fns, done) {
  const results = {};
  fns.forEach((fn, index) => {
    fn((result) => {
      results[index] = result;
      if (Object.keys(results).length === fns.length) {
        done(results);
      }
    });
  });
}

const parallel = (funcArray, doneAll) => 
  Promise.all(funcArray.map(f => new Promise(r => f(r)))).then(doneAll)